Coordinates
Numeric value is not a part of LIDO charting standard, only the side-scale is there to help you in case you need them. Jeppesen does the same, IIRC.
EGLL
I suppose LIDO show them on the IAC because so does the
UK AIP.
Use case
When operating to an airport which is not covered by your FMS database, it may be very helpful to create a destination runway at times.
Achieved precision
The accuracy of FMS manual entries is limited by the input format to one-tenth of a minute. I.e. N 51 28.7 - W000 29.1. Wheter you read from a scale on AGC, or read the AIP values you still get an error, no matter how accurate your data source is. You simply cannot enter N 51 28.650 W000 29.101.